Roof covering



T. A. LAWSON ROOF COVERING April 10, 1945.

Filed May 2, 1942 wwwa;

. INVENTOR THOMAS ,4. An/.90N

ATTORNEY Patented Apr. 10, 1945 UNITED vs'rA'ifaws, PATENT AoFFlcr.

ltooF covEmNG Thomas A. Lawson, San Francisco, Calif.

Application May 2, 1942, serialNc. 441,491 z claims. (ci. s-a5) Thisinvention re to improvements in l-'toof Coverings and mo particularly tocomposite fireproof shields for roof coverings.

Among the objects of the invention isthe provision of a stratifiedshield composed of noncombustible granular minerals, adapted to beeasily applied to conventional hat roofs.

. Another object is the protection of theunderlying roof with a friableshield that may be easily removed to permit access to any portion of theroof for repairing. v

Another object is the utilization of easily obtainable materials in thecomposition of the shield to facilitate its application to the roof without specialized skill and at a reasonable price.

A further object is the accomplishment of the above objects with minimalweight per square foot of roof area.

Other objects and advantages will appear as the description progresses,

In the specification and the accompanying drawing the invention isdisclosed in its preferred form. But it is to be understood that it isnot limited to this form because it may be embodied in modificationswithin the spirit of the invention as defined in the claims followingthe description.

In the one sheet of drawings:

Fig. 1 is a. fragmentary detail of a portion of a roof adjacent the sidewall, having this invention applied thereto and shown in verticalsection. i

the upper portions of the surrounding wall.

The conventional roof covering consists of the heavy fiber sheets Iimpregnated with water proofing, such as vfluid asphalt, tar or thelike. The edge of the first side sheet is folded up the side wall andattached to the coping board 4. The edge of the next sheet 5 isoverlapped to form a seam at 5' that is nailed to the sheathing.

The top surface of the fiber sheets is then given a heavy coating of tarI brushed on in a manner to seal all the seams 5' and the upper edges ofthe tar coating 6 is still i'iuid or tacky a layer of/ coarse and neygravel 'I is spread evenly over the treated area. The gravel adheringto the coating 6 tends to anchor all the gravel against displacement bypassing winds. The above describes a conventional flat gravel roof,having just enough inclination to provide drainage. There are variousmodifications of the above, such as prefabricated sheets having a topcoating of fine slate aggregate instead of the pebble'gravel l, to whichthe present invention is equally applicable.

The heat from a glowing cinder or rebrand falling upon such a roof willrelease volatile gases from the tarr coating 6, feeding the flames untilthe fabric sheets 5 are ignited and the fire reaches the underlyingsheathing l.

The present invention consists of the composition and the method ofapplying a composite fireproof shield for any conventional form of datroofing. The first step in the method is to distribute evenly over thesurface of the gravel layer l, a mat of asbestos fiber, rock wool orsimilar Y pairing.

the sheets where they join the coping I. While non-inflammable fibrousmaterial. This fluffy layer is then tamped or patted down until itpenetrates into the interstices in the gravel layer l, beneath. A thinlayer 9 of Portland cement or the like, is then sprinkled evenly overthe mat 8 and sprayed lightly with water to form a thin skin of neatcement on the surface which gradually seeps into the fibers of the mat,but not enough to destroy the friability of the mat when the cementsets, but Just enough to integrate the fibers to overcome the naturaliiufliness. The layer of gravel or fine aggregate Ill is then evenlydistributed over the top of the mat 8. A layer of Portland cement isthenevenly distributed over lthe surface of the top gravel layer l0 andlightly sprayed with water, just enough to carry the pulverized cementdown into the interstices in the .gravel layer I0, and leave acementitious glaze on its top surface.

The fibrous mat; B need not be. over to 1/2 an inch thick. It ismechanically keyed tc the gravel layer l, but it does not adherethereto, because of the poor adhesive qualities of Portland cement. Thisis desirable because it enables the easy removal of any portion of thereproof shield 8-9-I0 to expose the roofing l-'B--S for re- Thereprooing shield 8-9-l0 is not intended to contribute to thewaterproofing of the roofing beneath, except to an incidental extent. Ithas the advantage of thermal insulation, preventing the loss of heatfrom beneath the roof, and against the penetration of sunheat fromabove.

Where the coping such as I, is inammable it is good practice to cover itwith metal or asbestos sheeting such as Il, having its lower edge I2,folded outward beneath the mat l. Such sheeting should be continuedupward and over the top of the coping and secured by tacking oradhesion.

The porous mat l formed in the manner described, is superior toprefabricated sheets of asbestos or other non-inflammable material,because it is not subject. to lifting by winds blowing across it. A moredense layer will tend to lift off the roof surface due to suction and betorn or displaced. l

If preferred the ber forming the mat 8 can be premoistened with waterand spread over the roof like plaster. This is advantageous whileworking in windy weather.

Having thus described this invention what is claimed and desired tosecure by Letters Patent is:

1. The method of reprooiing a roof having a conventional coveringconsisting of superposing a continuous non-adhesive mat of brousnoninammable material on said covering; applying a coating of Portlandcement to the top surface of said mat; superposing a layer of loosegravel on top of said mat; applying a coating of dry Portland cement ontop of the gravel on said mat; and then moistening said structure withWater.

2. In combination with a roof having conventional gravel roof covering;a continuous shield composed of noninlammable fibrous materialimpregnated with Portland cement to form a nonadhesive friable matoverlying said covering; a layer of Portland cement applied to said mat:and a top layer of gravel embedded in said layer of cement.

THOMAS A.. LAWSON.

